1. Field of the Invention
The invention relates to a control apparatus and a control method for an automatic transmission.
2. Description of Related Art
An automatic transmission is configured to selectively establish any one of a plurality of speeds. The speed of the automatic transmission is automatically controlled based on a shift map stored in advance, and a quantity of state of a vehicle in which the automatic transmission is mounted. The quantity of state of the vehicle is a quantity of state that is typically indicated by an accelerator operation amount and vehicle speed as parameters. The shift map is a plurality of upshift lines and a plurality of downshift lines both corresponding to a plurality of speeds, for example.
Japanese Patent Application Publication No. 2008-240561 (JP 2008-240561 A) describes an automatic transmission capable of establishing six speeds. i.e., 1st speed to 6th speed, which executes a downshift from N speed (where N is a natural number of 3 of higher) into a speed two or more speeds lower, by skipping N−1 speed that is one speed lower (that has a larger speed ratio). Hereinafter, this type of downshift may also be referred to as a “skip downshift” or a “first downshift”.
When a skip downshift from N speed into N−2 speed is executed, a downshift line obtained by temporarily superimposing a downshift line for changing from N speed to N−1 speed (hereinafter referred to as a “N−1 speed downshift line”) and a downshift line for changing from N−1 speed to N−2 speed (hereinafter referred to as a “N−2 speed downshift line”) is hypothetically created as a skip downshift line for changing from N speed to N−2 speed (hereinafter referred to as a “N−2 speed skip downshift line”), and a skip downshift from N speed into N−2 speed is executed after the quantity of state of the vehicle changes from being below the N−2 speed skip downshift line to above the N−2 speed skip downshift line.